A simplification of gas clathrate hydrate thermochemistry using the Thermodynamic Difference Rule (TDR). Part 4. Further extension of the TDR to temperatures other than 298 K and validation of the similarity found between inorganic hydrate and clathrate hydrate TDR equations

Abstract

Abstract This paper continues the investigation of the role of TDR equations as they apply to heat capacity data. A TDR equation is proposed and investigated using heat capacity data for CH4·6H2O, C2H6·7.67H2O, C3H8·17.0H2O, Xe·5.90H2O, Xe·6.29H2O and Kr·6.10H2O Variation of Θ C p ( H 2 O,s - g ) / J K - 1 mol - 1 is examined as a function of temperature, T/K by fitting a linear regression line. The main conclusion of the paper is that the equation: [ C p ( M p X q . n H 2 O,s,T ) - C p ( M p X q ,g,T ) ] = [ 0.1378 T / K + 0.7972 ] n represents a TDR equation capable of yielding an estimate of heat capacity, C p ( M p X q . n H 2 O,s,T ) for any general hydrate (gas hydrate or conventional inorganic hydrate) in the temperature, T/K, range 100–300 K, with errors not usually greater than 10% and often considerably less than this. So vast are the capabilities of the TDR that a proposal is made for the creation of a vast database of entirely self-consistent thermodynamic data for hydrates and their parents without use of further experimental calorimetry. The TDR is used to determine an improved value for the heat capacity of the tetrahydrate of beryllium sulfate: C p ( BeSO 4 · 4 H 2 O,s ) / J K - 1 mol - 1 = 247.1 .